The present invention is related to microelectromechanical systems (MEMS) and the fabrication thereof, in general, and more specifically, to a microneedle array module and its fabrication.
Targeted drug delivery or the application of a high concentration of one or more drugs to a specific target area within the body has become of paramount importance to the fight against tumors, restentosis and similar life threatening medical conditions. Generally, these target areas are reachable through the walls of the blood vessels of the body. Present systems use a catheter with an imaging device to locate the target area. Once located, a specific drug or drugs are delivered to the targeted vessel wall area. But, this process has posed serious problems.
One approach provides a drug inside a perforated balloon at the end of the catheter. When the balloon reaches the target area, it is inflated causing the drug to be released through the perforations of the balloon locally around the targeted walls of the vessel. This perfusion of the drug at the surface of the vessel walls relies heavily on the drug being absorbed quickly and efficiently by the vessel walls at the target area. However, in some cases the drug may not be absorbed by the vessel walls very effectively. In these cases, the drug may be caused to move downstream with the blood stream which may cause adverse medical effects to portions of the body not intended to receive the drugs, especially at such high concentrations. The drugs may also be diluted in this delivery process and lose their effectiveness. In any event, these relatively expensive drugs may not be achieving their intended purpose.
Some recent drug delivery systems, like those proposed in the U.S. Pat. Nos. 5,112,305; 5,242,397; 5,681,281; 5,713,863 and 5,746,716, for example, provide for a studded balloon catheter. The balloon or portions thereof contain the drug or drugs to be delivered to the target area. When the balloon reaches the target area, it is inflated causing the studs to press against the vessel walls. The drug is then forced from the balloon through the studs into the surface of the vessel walls. However, the stud protrusions of the balloon are not needles and thus, are not very efficient at puncturing the vessel walls, especially at depths adequate for injecting the specific drug.
What is needed for effective drug delivery is an array of microneedles of sufficient length which may be deployed to the target site within the body and adequately penetrate the vessel walls thereat to permit the drug to effectively act on the target area at the high concentrations intended. Such an array structure may also be used transdermally for drug delivery as well.
In accordance with one aspect of the present invention, a microneedle array module comprises a multiplicity of microneedles affixed to and protruding outwardly from a front surface of a substrate to form the array, each microneedle of the array having a hollow section which extends through its center to an opening in the tip thereof. The substrate includes an array of holes which align with the hollow sections of the microneedles and extend through the substrate to a back surface thereof, whereby a liquid applied to the back surface of the substrate may be forced through the holes in the substrate and out through the tips of the microneedle array thereof. In one embodiment, the substrate includes a reservoir well in the back surface thereof. The well extends over the array of holes in the back surface and may be covered by a layer of material which is affixed to the back surface peripheral the well, the layer including an interconnecting passageway to the well.
In accordance with another aspect of the present invention, a method of fabricating a microneedle array module comprises the steps of: providing etch resistant mask layers to one and another opposite surfaces of a substrate to predetermined thicknesses; patterning the etch resistant mask layer of the one surface for outer dimensions of the microneedles of the array; patterning the etch resistant mask layer of the other surface for inner dimensions of the microneedles of the array; etching unmasked portions of the substrate from one and the other surfaces to first and second predetermined depths, respectively; and removing the mask layers from the one and the other surfaces. One embodiment of the method includes the steps of: providing an etch resistant mask layer to the other surface of the substrate to a predetermined thickness; patterning the etch resistant mask layer of the other surface to define a reservoir region in the substrate; and etching away the unmasked reservoir region of the substrate to form a reservoir well in the other surface of the substrate. A layer of material may be provided to the other surface to enclose the reservoir well and a passageway is provided through said layer to the well region.